I am trying to understand various licenses. I usually do small projects in which I use say a jquery plugin which is under MIT license. Now is it okay for me to do the same? Is there a sort of a matrix which compares all the licenses (major ones atleast) and tells me just one thing:

Royalty-free ability to use in commercial project? (no back-links or anything)
(I dont mind keeping their copyright text on top of the code)

Update Thank you very much for all your answers. Also wondering what exactly do they mean by LGPL i.e. lesser GPL. I read the license, but could not seem to understand what exactly it means.

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6 Answers
6

A software license agreement is a contract between a producer and a user of computer software which grants the user a software license. Most often, a software license agreement indicates the terms under which an end-user may utilize the licensed software, in which case the agreement is called an end-user license agreement or EULA. When the software license agreement is between the software licensor and a business or government entity, it is often implemented as a specialized form of contract with many clauses unique to the license and the nature of the software being licensed.

The GNU General Public License (GNU GPL or simply GPL) is a widely used free software license, originally written by Richard Stallman for the GNU project. The GPL is the most popular and well-known example of the type of strong copyleft license that requires derived works to be available under the same copyleft. Under this philosophy, the GPL grants the recipients of a computer program the rights of the free software definition and uses copyleft to ensure the freedoms are preserved, even when the work is changed or added to. This is in distinction to permissive free software licenses, of which the BSD licenses are the standard examples.

The MIT License is a free software license originating at the Massachusetts Institute of Technology (MIT), used by the MIT X Consortium.

It is a permissive license, meaning that it permits reuse within proprietary software on the condition that the license is distributed with that software. The license is also GPL-compatible, meaning that the GPL permits combination and redistribution with software that uses the MIT License.

According to the Free Software Foundation, the MIT License is more accurately called the X11 license, since MIT has used many licenses for software and the license was first drafted for the X Window System.

Creative Commons licenses are several copyright licenses released on December 16, 2002 by Creative Commons, a U.S. non-profit corporation founded in 2001.

Many of the licenses, notably all the original licenses, grant certain "baseline rights", such as the right to distribute the copyrighted work without changes, at no charge. Some of the newer licenses do not grant these rights.

Creative Commons licenses are currently available in 43 different jurisdictions worldwide, with more than nineteen others under development. Licenses for jurisdictions outside of the United States are under the purview of Creative Commons International.

+1. A nitpick: copyright licenses for free software are not necessarily contracts or agreements, technically speaking, since the user (receiver of the code) does not need to explicitly agree to them. That rarely matters outside the court room, though.
–
Lars WirzeniusApr 30 '09 at 5:45

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You should probably note that Creative Commons are not recommended for software because they say nothing about source code, whereas software licenses were specifically designed for that purpose. Creative Commons licenses are usually more for content, i.e. audio, images, etc.
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Chris LutzApr 30 '09 at 5:48

The following link http://www.opensource.org/licenses, posts all licences that confirm to the Open Source standard. This means all licences here are royalty free and would not request you for a backlink/ad etc. You may have to keep the copyright files/text in your software.

CC, or Creative Commons (http://creativecommons.org), is about content, one authors, and not generally for the code. It generally applies to documentation or forums like SO. Again there are different versions of CC, but, none of them requires back-links/ads, at max only attribution.

The GNU Project has two principal licenses to use for libraries. One
is the GNU Lesser GPL; the other is the ordinary GNU GPL. The choice
of license makes a big difference: using the Lesser GPL permits use of
the library in proprietary programs; using the ordinary GPL for a
library makes it available only for free programs.

The GPL v3 is a spaghetti licence. Here's my attempt to reorganise it. (The numbers in square brackets refer to the original numbers for sections, and in some cases paragraphs and sentences. These are all numbered according to the GPL convention of 0 meaning first, so, e.g. 10p0s0 means section 10, paragraph 0, sentence 0, or in other words the first sentence of the first paragraph of section 10.)

Definitions. [0, 1]

Receiving a Licence.

1.1. License grant is given upon receiving the Program. [10p0s0, 2p0s0, 11p0-2&7, 3p0]

a. License acceptance is implied by modifying or propagating. [9]

b. No warranty is provided, unless in writing for a fee. [15, 16, 17]

c. Additional liability disclaimers may apply. [7a]

d. Additional publicity restrictions may apply. [7d]

e. License adherence is not excused by other obligations. [12]

f. License termination may result from license breach. [8]

1.2. Additional permissions may apply. [7p0, 7p9s0-1, 14]

Using the Program.

2.1 Using the unmodified Program and fair use are unlimited. [2p0s1-3]

Especially the GPL is difficult to summarize shortly. I'll try anyway: You can use GPL code in your product royalty-free as long as the code is used stand-alone, e.g. a GPL database or a processing tool. But if your product is "based" on the GPL code, i.e. linked with it and extending its functionality, then your product must be under GPL too.

Being under GPL means everyone using the product must be allowed full access to the source, too, including the right to re-distribute the code, verbatim or modified. While strictly speaking the GPL allows you to charge customers for the product, this effectively means you cannot sell the product for profit. GPL evangelists claim you could sell support or documentation, but I have some issues with that notion I will not elaborate upon here. (First class flaimbait...)

For your purposes, you will want to look for BSD or MIT licensed code. GPL is generally not suitable for use in commercial projects (this is a broad generalisation, there are situations where it is appropriate!). CC does not usually apply to software.